Vertical Seismic Profile (VSP) analysis is a technique commonly used to conduct geophysical surveys of subterranean features. For instance, VSP analysis can be used to image the earth's subsurface in the proximity of a wellbore during the drilling or operation of a well. In an example implementation, one or more seismic energy sources are located at the surface and one or more seismic detectors are located within a wellbore. Information regarding the subsurface is determined based on the detection of reflected seismic energy that originates from the seismic energy sources at the surface.
The processing of a VSP includes several steps, usually including a final step of depth migration. In order to properly process and image VSP data using depth migration, a velocity model of the subsurface must be known or derived. A velocity model refers to the velocity of energy propagation across the examined subsurface.